Burn-in gumming composition for offset printing plates

ABSTRACT

A burn-in gumming composition for irradiated and developed offset printing plates comprises water and a water-soluble polymer or copolymer for protecting the plate surface during the burning-in step and during long-term storage. The polymer or copolymer used contains sulfonic acid groups and/or alkali metal sulfonate or ammonium sulfonate groups.

This application is a division of application Ser. No. 07/241,790, filedSept. 6, 1988, which is a division of application Ser. No. 06/928,392,filed Nov. 10, 1986.

BACKGROUND OF THE INVENTION

The invention relates to a burn-in gumming composition for irradiatedand developed offset printing plates.

Offset printing plates in general comprise: (a) a two-dimensionalcarrier material of metals and/or plastics, the surface of which can bemodified, for example, by roughening (etching) and/or anodic oxidation,and (b) at least one radiation-sensitive (photosensitive) coating(reproduction layer). Particularly in the case of positive-workingreproduction layers, but in principle also with negative-workingreproduction layers, the preparation of a printing form with the basicprocess steps of irradiation, development and gumming (preserving,desensitizing) also includes a burn-in step between the last two steps.Applied to positive-working reproduction layers, the procedure can beillustrated as follows. During the imagewise irradiation (exposure),those parts of the reproduction layer which are struck byelectromagnetic energy (light) become soluble, and the unaffected partsremain insoluble (in each case relative to the developer to be used). Asa result of the first-mentioned parts being dissolved out in thedeveloping step, the non-image areas, which are water-bearing during thelater printing from the printing form, are formed on the surface of theprinting plate after the development of the irradiated reproductionlayer, and the image areas which are ink-bearing during later printingare formed from the last-mentioned parts. In practice, it has been foundthat heating of the irradiated and developed printing plate--dependingon the nature of the carrier material and/or the production layer--tomore than 180° C. can lead to longer print runs with the printing formthus resulting. This process is called "burning-in". The burning-inachieves a consolidation of the image areas, the latter becoming, forexample, insoluble in the usual organic solvents and resistant to theaction of chemicals.

During burning-in, constituents of the image areas (i.e., of thereproduction layer), for example, constituents of the binder, can alsopass into the non-image areas and hence adversely affect the hydrophiliccharacter of the latter, leading, for example, to toning (absorption ofprinting ink in the non-image areas). Therefore, it was necessary, inthe initial phase of using a burning-in step, to remove the impuritiesin the non-image areas again by means of relatively aggressivesolutions.

In the course of time, so-called "burning-in aids" were developed whichat least facilitated this after-cleaning. However, as a rule,after-cleaning nevertheless still required cleaning of the non-imageareas with water before the actual printing process. The burning-in aidsknown from the state of the art include, inter alia, the followingexamples.

German Patent No. 2,318,286 (corresponding to U.S. Pat. No. 3,745,011)discloses a process for the preparation of negative resist images,wherein a photoresist is treated, after exposure and development andbefore a burn-in process, with a solution of a cycloaliphatic,heterocyclic, or aromatic polycarboxylic acid or an aromatic sulfonicacid. The photosensitive layers of the photoresists used contain naturalproteins, such as fish glue, and ammonium bichromate. This treatmentbefore burning-in is intended to: (a) lower the burning-in temperature;(b) increase the etch resistance of the resist image; and (c) improvethe strippability of the resist image or the applied photoresist. Theacids used include, inter alia, p-toluenesulfonic acid,2-napthalenesulfonic acid, naphthalene-1,8-disulfonic acid,benzenesulfonic acid, and 1,3-benzenedisulfonic acid, which are employedpreferably in the form of a 1 to 25% solution. Steel is used exclusivelyas the carrier material for the coating with photoresist. Theapplication for printing plates and the special problems with burning-inthat case are not mentioned.

German Patent No. 2,530,422 (corresponding to British PatentSpecification No. 1,513,368) discloses a process for the preparation ofprinting forms, plates for printed circuits, integrated circuits and thelike, wherein the exposed and developed carriers are, before burning-in,provided with a protective layer at least on the non-image areas. Thisprotective layer remains on the carrier during burning-in and can, afterburning-in, be removed by means of water together with a precipitatewhich settles on the protective layer during burning-in. The protectivelayer is applied in the form of an about 2.5 to 45% aqueous solution ofone of the following compounds: sodium dodecylphenoxybenzenedisulfonate,a sodium salt of an alkylated naphthalenesulfonic acid, disodiummethylenedinaphthalenedisulfonate, sodium dodecylbenzenesulfonate, asodium salt of a sulfonated alkyldiphenyl oxide, an ammoniumperfluoroalkylsulfonate, a potassium perfluoroalkylsulfonate, sodiumdioctylsulfosuccinate, sodium di-(methylamyl)-sulfosuccinate, andlithium nitrate.

In British Patent Specification No. 1,575,200 a water-solublehydrocolloid from the group comprising gum arabic, sodiumcarboxymethylcellulose, or alginate is also added to an aqueous solutionfor producing the protective layer before burning-in, in addition to oneof the compounds listed above. The mixture of substances used isintended to comprise 85 to 98% by volume of one of the compounds knownfrom British Patent Specification No. 1,513,368, and 2 to 15% by volumeof one of the hydrocolloids, and it is employed in a 10 to 50% by volumeaqueous solution. After burning-in, the printing forms are washed withwater and can then be clamped into a printing press.

The burn-in aid according to German Patent No. 2,625,336 (correspondingto U.S. Pat. No. 4,063,507) is boric acid or a borate and is employed insolid form or preferably in a 3 to 10% aqueous solution.

According to German Offenlegungsschrift No. 2,626,473 (corresponding toBritish Patent Specification No. 1,555,233), it is possible, in place ofthe compounds already described above as suitable for the burning-in ofprinting plates (burn-in aids), also to use, inter alia, varioushydrophilic polymers such as gum arabic, dextrin, polyvinyl alcohol,cellulose ethers, homopolymers and copolymers based on acrylic ormethacrylic acid or a copolymer of alkyl acrylate andvinylmethylacetamide or also salts of organic acids such as di-sodiumanthraquinone-2,7-disulfonate, tri-sodiumnaphthalene-1,3,5-trisulfonate, tri-sodium1-naphthylamine-4,6,8-trisulfonate, or tri-sodium1-naphthol-3,6,8-trisulfonate. The compounds are used in aqueoussolution in a concentration from 0.1% up to saturation.

European Patent Application No. 0,043,991 (corresponding to U.S. Pat.No. 4,355,096) lists amines containing carboxyl groups, such asethylenediaminetetraacetic acid, nitrilotriacetic acid or salts thereofas burn-in aids, and U.S. Pat. No. 4,191,570 lists salts or salt-likereaction products of naphthalene, formaldehyde and sulfuric acid.

However, all the known burn-in aids still have serious disadvantages.For example, they can effect a reduction in the oleophilic character ofthe image areas, and they can lead to staining of the printing platesurface and, particularly in the case of insufficient postcleaning withwater or aqueous developer solutions, to interference with thewater/printing ink balance during the later printing. In operatinginstructions for the use of many of the known burn-in aids, theseproblems are specifically pointed out, and it is stated that theseproblems can be overcome, for example, by dry rubbing of the printingplate surface before burning-in, by careful rinsing or even (for examplein European Patent Specification No. 0,012,956 (corresponding to U.S.Pat. No. 4,265,999)) or by providing hydrophilic properties bypost-treatment/cleaning with an aqueous solution of a hydrophilicpolymer such as polyvinylphosphonic acid. Such special post-treatmentsproviding hydrophilic properties, or one of the conventional gumming(preserving) post-treatments are possible in principle, but require anadditional working step in the preparation and use of a printing form. Acombination of the two steps in a burn-in gumming is described inBritish Patent Specification No. 1,575,200, described above, but itstill leads to a large consumption of paper in the printing press as,without additional intermediate cleaning, the printing form is too slowto run clean.

In European Patent Application No. 0,155,620, a burn-in gumming isproposed which comprises several components, including a hydrophilicpolymer, a water-soluble organic carboxylic or sulfonic acid or one oftheir water-soluble salts, a hydroxycarboxylic acid and/or saltsthereof, an alkanediol and a surfactant. A printing form treated withthis burn-in aid need no longer be washed off after burning-in but canbe clamped directly into the printing press. In this case, a relativelylarge number of components is employed, and it can happen that, in theevent of unduly thick preservation, as is frequently the case inpractice with manual treatment, the printing stencil can be extensivelydamaged during burning-in, so that perfect printing of long runs is nolonger possible.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a burn-ingumming composition which does not have the aforementioneddisadvantages, which prevents precipitation of impurities on the platesurface during heating of the printing form, which protects the printingform from contamination during storage, and which keeps the non-printingsurface areas permanently hydrophilic.

In accomplishing the foregoing objects, there has been provided inaccordance with one aspect of the present invention a burn-in gummingcomposition for irradiated and developed offset printing plates, usedfor protecting the plate surface during the burning-in step and duringlong-term storage, comprising an aqueous solution comprising water and awater-soluble polymer or copolymer, wherein the polymer or copolymercomprises monomers selected from the group consisting of sulfonic acids,alkali metal sulfonates, and ammonium sulfonates.

In another aspect of the invention, there is provided a method forburning-in irradiated and developed offset printing plates comprisingthe steps of coating at least one surface of an irradiated and developedoffset printing plate with a burn-in gumming composition comprising anaqueous solution comprising water and a water-soluble polymer orcopolymer, wherein the polymer or copolymer comprises monomers selectedfrom the group consisting of a sulfonic acid, an alkali metal sulfonate,and an ammonium sulfonate, and then heating the coated printing platefor a sufficient time to effect burning-in, wherein the temperature towhich the coated printing plate is heated ranges from about 150° to 300°C., and preferably from about 200° to 230° C., for between 0.5 and 10minutes in order to effect burning-in.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention starts from a burn-in gumming composition for irradiatedand developed offset printing plates, comprised of water and awater-soluble polymer or copolymer. In the burn-in gumming according tothe invention, the polymer or copolymer contains sulfonic acid groupsand/or alkali metal sulfonate or ammonium sulfonate groups.

According to the invention, those polymers or copolymers areparticularly suitable which contain, as monomer units, styrenesulfonicand/or methylstyrenesulfonic acids in the form of their water-solublesalts. Polymers comprising, as monomer units, aliphatic sulfonic acidgroups as such, or in the form of their water-soluble salts, are alsosuitable, such as, for example, polyvinylsulfonic acid and its alkalimetal salts, or copolymers which contain, as monomer units,vinylsulfonic acid or acrylamidopropanesulfonic acids or salts thereof.Polymers comprising partially or fully saponified polyvinyl acetate arealso suitable, the polyvinyl alcohol units being partially acetalizedwith butyraldehyde-4-sulfonic acid.

The polymers or copolymers according to the invention preferably have amolecular weight between 1,500 and 500,000.

The polymer or copolymer used according to the invention combines, interms of effect, in a single component the components hitherto employedin the known burn-in gumming compositions (a) for avoiding contaminationof the background during burning-in, and (b) for preserving the printingform for the purpose of storage for a prolonged period. The burn-ingumming composition according to the invention contains, in particular,1 to 50% by weight, and preferably 3 to 20% by weight, of the alkalimetal or ammonium salt of a sulfonated polystyrene.

In different embodiments, the burn-in gumming compositions can alsocontain hydroxypolycarboxylic acids, such as citric acid and/or itssalts, in a proportion of 0.10 to 5%, and surfactants (preferablyanionic or non-ionic surfactants) such as alkylarylsulfonates (forexample di-sodium diisobutylnaphthalene-disulfonate), or a naturalsurfactant (for example saponin) in a proportion of 0.01 to 5%.

The procedure when using the burn-in gumming composition can be suchthat the surface or, in the case of double coating with a reproductionlayer, both surfaces, of the irradiated and developed offset printingplate are rubbed with a dabber which has been impregnated with theburn-in gumming composition. However, other methods of application, suchas dipping, spraying, whirler-coating or pouring-on, are also possible,and can be carried out either by hand or by automatic processingmachines. Advantageously, the surface of the printing plate providedwith the burn-in gumming composition is dried before burning-in. Dryingcan also take place, however, during the subsequent burning-in.

The layer weight of the burn-in gumming composition after drying isgenerally in the range from 0.05 to 20 g/m². The printing plate thustreated is then burned-in at a temperature of 150° to 300° C., and inparticular 200° to 230° C., in a burning-in stove, with the burning-intimes usually being 0.5 to 10 minutes. Apart from the hot-air ovens usedin practice, other types of treatment have also been described, mostrecently for example, irradiation with quartz-halogen lamps according toGerman Patent No. 1,955,378, with infrared radiation according to GermanPatent No. 2,201,936 or with UV lamps according to GermanOffenlegungsschrift No. 3,110,632.

The conventional offset printing plates used in practice, of metaland/or heat-stable plastic, can be treated with the burn-in gummingcomposition according to the invention, but the latter is particularlysuitable for those offset printing plates which have a mechanically,chemically, and/or electrochemically roughened and, if appropriate,anodically oxidized carrier material of aluminum or one of its alloys.These carrier materials can carry negative-working or positive-workingreproduction layers which contain one of the known radiation-sensitivecompounds such as diazo, diazonium or azido compounds, orphotopolymerizable compounds (see, for example, Jaromir Kosar,"Light-sensitive systems", John Wiley & Sons, New York, 1965). However,the burn-in gumming composition according to the invention isparticularly suitable for positive-working reproduction layers which ingeneral contain, in addition to the actual radiation-sensitive compound,resins, in particular novolaks or resols, and also various othercomponents such as dyes, adhesion promoters or leveling agents. Theradiation-sensitive compounds in these reproduction layers include inparticular the o-quinone-diazides, preferably o-naphthaquinone-diazidessuch as 1,2-naphthoquinone-2-diazide-sulfonic acid esters or amideswhich can be of low or higher molecular weight. In this connection, see,for example, German Patent Nos. 854,890, 865,109, 879,203, 894,959,938,233, 1,109,521, 1,144,705, 1,118,606, 1,120,273, 1,124,817 and2,331,377 and European Patent Application Nos. 0,021,428 and 0,055,814.

For positive-working copying layers, materials based on compoundscleavable by acid can also be used very successfully. Copying materialof this type is known and described in, for example, U.S. Pat. Nos.3,779,778 and 4,101,323, German Patent No. 2,718,254 and GermanOffenlegungsschriften No. 2,928,636 and No. 2,829,512 and No. 2,829,511.They contain, as the compounds cleavable by acid, orthocarboxylic acidderivatives, monomeric or polymeric acetals, enol ethers oracyliminocarbonates. As the radiation-sensitive acid-releasingcompounds, they predominantly contain organic halogen compounds, inparticular s-triazines substituted by halomethyl groups, or2-trichloromethyl-1,3,4-oxadiazoles.

The burn-in gumming composition according to the invention provides theeffect, known from the burn-in aids, of easy removal of contaminationfrom the non-image areas of offset printing plates. In addition,however, it obviates washing-off of the protective layer applied and/orapplication or renewal/touching-up of gumming (preserving). A printingform provided with the burn-in gumming according to the invention runsclean in the printing press in a surprisingly short time and ensuresrapid absorption of ink by the image areas, coupled with simultaneousfreedom of the non-image areas from tone.

It is a particular advantage that, in contrast to the burn-in aidshitherto known, the contamination of the background which occurs duringthe burn-in step is prevented, and permanent preservation of theprinting form is achieved with only a single component. A furtheradvantage is that the burn-in gumming compositions according to theinvention do not form any sparingly soluble alkaline earth metal salts,so that no further complex formers, such as, for example,nitrilotriacetic acid, which very often are the cause of the attack onthe layer during burning-in, need be added to the burn-in gummingcomposition.

In the preceding description and the following examples, percent dataare always percent by weight, unless otherwise stated, and parts byweight have the same relationship with parts by volume as the g with thecm³.

EXAMPLE 1

An electrochemically roughened and anodized aluminum plate is coatedwith a positive-working radiation-sensitive mixture of:

1.200 parts by weight of the esterification product obtained from 1 moleof ethoxyethyl 4,4-bis-(4-hydroxyphenyl)-n-valerate and 2 moles of1,2-naphthoquinone-2-diazide-5-sulfonic acid chloride,

6.800 parts by weight of a novolak prepared by condensation of atechnical cresol mixture with formaldehyde, having a melting point of108° to 118° C.,

0.070 part by weight of crystal violet, and

0.200 part by weight of 1,2-naphthoquinone-2-diazide-4-sulfonic acidchloride in

50.00 parts by weight of ethylene glycol monomethyl ether, and

50.00 parts by weight of tetrahydrofuran. Before application of thelight-sensitive copying layer, the anodized carrier had been treatedwith an aqueous solution of 0.1% by weight of polyvinylphosphonic acid.

The offset printing plate thus prepared, having a reproduction layerwith a weight of 2.30 g/m², is exposed imagewise under a transparentpositive original and then developed with the following solution:

5.3 parts by weight of Na₂ SiO₃.9 H₂ O,

3.4 parts by weight of Na₃ PO₄ 4.12 H₂ O, and

0.3 parts by weight of NaH₂ PO₄ anhydrous in 91.0 parts by weight of H₂O. As a result of the development, those areas of the reproduction layerwhich have been struck by the light are removed, and the unexposed partsremain as image areas on the carrier material, so that a printingstencil corresponding to the original is obtained. About 100,000 perfectprints can be obtained in a printing press from a printing form thusprepared. In order to attain a multiple of this length of run, theprinting plate must also be burned-in in a manner known per se. For thispurpose, the exposed and developed printing plate is wiped, by means ofa dabber, with the following burn-in gumming composition comprised of 5%aqueous solution of the sodium salt of a polystyrenesulfonic acid havinga molecular weight of about 70,000, and dried, with care being taken toensure that a coherent film is formed across the entire surface of theprinting form.

The printing form provided with a protective layer is then burned-in for5 minutes at 230° C. in a commercially available hot-air oven. Theprinting form thus prepared can be clamped immediately into the printingpress and subjected to the conventional printing process without itbeing necessary to remove the protective layer first with water and/orto treat the printing form, if appropriate, again with a preservingagent such as, for example, gum arabic. Already after 4 revolutions ofthe dampening rollers and inking rollers of the printing press, completeink absorption by the printing stencil coupled with simultaneous freedomof the background from tone is achieved, so that perfect prints areobtained at the latest after 6 sheets of paper ("spoilage").

If the burn-in gumming composition used according to the invention inExample 1 is replaced by one of the examples according to EuropeanPatent Application No. 0,155,620, perfect prints are obtained only after15 to 20 sheets of paper (spoilage) under the same test conditions. Evenwith a relatively thick preservation of the printing form with theburn-in gumming composition indicated in Example 1, the printing stencilis not damaged during the burn-in process, so that perfect inkabsorption is ensured also during continued printing. By contrast, theburn-in aids indicated by European Patent Application No. 0,155,620show, in the event of unduly thick preservation, and above all in theareas where drops of the burn-in gumming were not distributed butremained as dried-up spots, extensive attack on the layer duringburning-in.

If a presensitized offset printing plate prepared according to Example 1is treated under the same test conditions before burning-in with anaqueous solution of 7% of gum arabic and 22% of di-sodiumdodecylphenoxybenzenedisulfonate according to Example 1 of BritishPatent Specification No. 1,575,200 and the printing plate thuspretreated is burned-in and clamped into the printing press withoutwashing off the protective layer, no perfect proof is obtained evenafter 100 sheets of paper have passed through. A similarlyunsatisfactory result is obtained if sodium carboxymethylcellulose isused in place of gum arabic.

Printing forms prepared according to German Offenlegungsschrift No.2,626,473 or German Patent No. 2,625,336 with, for example, Na₂ B₄ O₇ orNa₂ HPO₄ as the burn-in aid also cannot give a perfect proof if thecorresponding protective layers are not washed off with water before theactual printing process.

A further advantage of the polystyrenesulfonic acids used according tothe invention is that the latter form readily soluble alkaline earthmetal salts so that no turbidity is produced in the burn-in gummingcompositions even when large quantities of relatively hard water areadded. This is in contrast to many of the hitherto claimed burn-in aids,in which organic carboxylic, sulfonic or phosphonic acids are used, allof which form more or less sparingly soluble alkaline earth metal salts.If, for example, 100 ml of water of 35 degrees German hardness are addedto 1 ml of the burn-in aid indicated in Example 3 of European PatentApplication No. 0,155,620, or 1 ml of the burn-in aid indicated inExample 2 of British Patent Specification No. 1,513,368, considerableturbidity is produced after brief standing, whereas no turbidity isobservable under the same test conditions with the burn-in gummingcomposition claimed according to the invention even after addition of1000 ml of the same water. Such turbidity or precipitations in theburn-in gumming compositions, caused by entrained developer and/or waterresidues from the upstream tanks, can arise in particular in theautomatic processing units where exposure, development, and preservationare carried out in one working step.

The burned-in printing plate provided with the burn-in gummingcomposition according to the invention can also be stored at roomtemperature over a period of several months without the disadvantagesof, for example, a tone appearing in the image-free areas arising duringa printing run started at a later date.

In the examples which follow, further burn-in gumming compositions areindicated with which the printing plate prepared according to Example 1is treated before burning-in, perfect prints being obtained in theprinting press within relatively short time, similarly to Example 1.Unless specially noted, the preparation and processing of the printingplates thus obtained correspond to the conditions described in Example1.

EXAMPLE 2

The following burn-in gumming composition is used:

3.00 parts by weight of the sodium salt of a polystyrenesulfonic acidhaving a molecular weight of about 500,000, and

97.00 parts by weight of distilled water.

EXAMPLE 3

The following burn-in gumming composition is used:

4.00 parts by weight of the sodium salt of a polystyrenesulfonic acidaccording to Example 1,

1.00 parts by weight of calcium citrate,

0.20 part by weight of citric acid, and

94.80 parts by weight of distilled water.

EXAMPLE 4

The following burn-in gumming composition is used:

3.00 parts by weight of the sodium salt of a polystyrenesulfonic acidaccording to Example 2,

0.05 part by weight of the sodium salt of1,2-isopropylnaphthalenesulfonic acid (anionic surfactant), and

96.95 parts by weight of distilled water.

EXAMPLE 5

The following burn-in gumming composition is used:

4.00 parts by weight of a copolymer of styrenesulfonic acid (sodiumsalt) and maleic anhydride in a 3:1 ratio,

2.00 parts by weight of potassium citrate,

0.50 part by weight of citric acid, and

93.50 parts by weight of distilled water.

EXAMPLE 6

The following burn-in gumming composition is used:

5.00 parts by weight of a partially saponified polyvinyl acetate, thealcoholic groups of which are acetalized with butyraldehyde-4-sulfonicacid, and

95.00 parts by weight of distilled water.

EXAMPLE 7

The following burn-in gumming composition is used:

3.00 parts by weight of a copolymer comprised of 20%acrylamidopropanesulfonic acid and 80% vinylphosphonic acid, and

97.00 parts by weight of distilled water.

EXAMPLE 8

The following burn-in gumming composition is used:

5.00 parts by weight of a copolymer comprised of 40% vinylsulfonic acidand 60% vinylphosphonic acid, and

95.00 parts by weight of distilled water.

What is claimed is:
 1. An offset printing plate, comprising:a metalsupport; an irradiated and developed photosensitive layer on thesupport; and a burn-in gumming composition overlying the irradiated anddeveloped offset photosensitive layer for protecting the plate surfaceduring a burning-in step and during long-term storage, comprising anaqueous solution which comprises from about 1 to 50% by weight of awater-soluble polymer or copolymer, wherein the polymer or copolymercomprises monomers selected from the group consisting of styrenesulfonicacid, methylstyrenesulfonic acid, vinylsulfonic acid, acrylamidopropanesulfonic acid, vinyl acetate, and the water-soluble salts thereof.
 2. Anoffset plate according to claim 1, wherein the polymer or copolymercomprises monomers selected from the group consisting of styrenesulfonicacid and methylstyrenesulfonic acid.
 3. An offset plate according toclaim 2, wherein the polymer comprises an alkali metal salt of asulfonated polystyrene.
 4. An offset plate according to claim 2, whereinthe polymer comprises an ammonium salt of a sulfonated polystyrene. 5.An offset plate according to claim 2, wherein the copolymer comprises analkali metal salt of a copolymer of sulfonated styrene and maleicanhydride.
 6. An offset plate according to claim 2, wherein thecopolymer comprises an ammonium salt of a copolymer comprisingsulfonated styrene and maleic anhydride.
 7. An offset plate according toclaim 1, wherein the polymer or copolymer comprises monomers selectedfrom the group consisting of an aliphatic sulfonic acid.
 8. An offsetplate according to claim 1, wherein the polymer is selected from thegroup consisting of the alkali metal salts and ammonium salts ofpolyvinylsulfonic acid.
 9. An offset plate according to claim 1, whereinthe copolymer comprises monomer, selected from the group consisting ofvinylsulfonic acid and acrylamidopropanesulfonic acid.
 10. An offsetplate according to claim 1, wherein the polymer or copolymer comprisesacetal groups formed from an aldehydesulfonic acid.
 11. An offset plateaccording to claim 8, wherein the polymer or copolymer comprisesmonomers selected from the group consisting of a partially saponifiedpolyvinyl acetate and fully saponified polyvinyl acetate, wherein thepolyvinyl alcohol units of said polymer are at least partiallyacetalized with butylaldehyde-4-sulfonic acid.
 12. An offset plateaccording to claim 1, wherein the polymer or copolymer has a molecularweight of from about 1,500 to 500,000.
 13. An offset plate according toclaim 1, wherein the proportion of polymer or copolymer in the aqueoussolution is about 3 to 20% by weight.
 14. An offset plate according toclaim 1, further comprising a surfactant in an amount from about 0.01 to5% by weight.
 15. An offset plate according to claim 1, furthercomprising a hydroxypolycarboxylic acid in an amount from about 0.01 to5% by weight.
 16. An offset plate according to claim 1, furthercomprising a water soluble salt of a hydroxypolycarboxylic acid in anamount from about 0.01 to 5% by weight.
 17. An offset plate according toclaim 1, wherein the amount of said polymer or copolymer in the solutionresults in a dry layer weight of about 0.05 to 20 g/m².